Field of the Invention
The present invention relates to an internal combustion engine leakage detection apparatus and more particularly to an internal combustion engine leakage detection apparatus that detects leakage in an ignition plug of an internal combustion engine provided with a cylinder rest function.
Description of the Related Art
In recent years, the problems such as environment preservation and fuel depletion have been raised; measures for these problems have become big issues also in the automobile industry. As an example of the measure, in an internal combustion engine provided with two or more cylinders, there has been developed a so-called cylinder resting drive technology in which there is provided a cylinder resting function of resting fuel injection into part of the cylinders and valve driving and in which car driving is implemented only by the cylinders other than the resting cylinders.
In the foregoing cylinder resting drive, in many cases, the intake valve and the exhaust valve of a resting cylinder are fully closed in order to reduce the intake/exhaust loss of the internal combustion engine, i.e., the pumping loss thereof. Accordingly, the pressure inside of a hermetically sealed resting cylinder becomes negative as the piston moves; then, the oil or the like inside the crankcase of the internal combustion engine may intrude into the cylinder. Especially in the vicinity of the bottom dead center of the piston, the pressure inside of the hermetically sealed resting cylinder becomes largely negative; thus, oil or blowby gas intrudes into the resting cylinder from the crankcase. This phenomenon is referred as “oil rising”.
In the case where a cylinder resting drive is carried out for a long time, oil rising contaminates the ignition plug and hence leakage may be caused in the ignition plug. In other words, in the case where oil or blowby gas including an electrically conductive material such as metal powder, soot, or moisture attaches oneself to the ignition plug, a decrease in the insulating resistance value of the ignition plug causes an ignition current to leak. When the ignition current increases, in the worst case, the probability of a misfire is raised even when the all-cylinder drive is resumed after the cylinder resting drive and then fuel is injected into the resting cylinder that has been resting.
Accordingly, to date, as disclosed in Patent Document 1, for example, there has been proposed a technology in which at a time of and after the start of the cylinder resting drive of an internal combustion engine, the level of contamination, caused by oil rising, in the ignition plug of the resting cylinder is estimated and then the ignition plug of the resting cylinder is ignited for a time that is long enough to cancel the estimated contamination of the ignition plug so that the contamination of the ignition plug is cancelled.
To date, for example, as disclosed in Patent Document 2, as an apparatus for detecting leakage in an ignition plug of an internal combustion engine, there has been proposed a misfire detection apparatus in which an ion current detection circuit detects an ion current that flows when a voltage is applied to an ion produced as an inflammable fuel-air mixture in the internal combustion engine combusts and in which whether or not leakage exists in the ignition plug is determined based a leakage current included in the detected ion current.